Chemical synthesis plant

ABSTRACT

A plant, such as a hydrocarbon plant, is provided, which consists of a syngas stage for syngas generation and a synthesis stage where said syngas is synthesized to produce syngas derived product, such as hydrocarbon product. The plant makes effective use of various streams; in particular CO2 and H2. A method for producing a product stream, such as a hydrocarbon product stream is also provided.

TECHNICAL FIELD

The present invention relates to a plant, such as a hydrocarbon plant,with effective use of various streams, in particular carbon dioxide. Amethod for producing a product stream, such as a hydrocarbon productstream is also provided. The plant and method of the present inventionprovide overall better utilization of carbon dioxide.

BACKGROUND

Carbon capture and utilization (CCU) has gained more relevance in thelight of the rise of atmospheric CO₂ since the Industrial Revolution. Inone way of utilizing CO₂, CO₂ and H₂ can be converted to synthesis gas(a gas rich in CO and H₂) which can be converted further to valuableproducts like alcohols (including methanol), fuels (such as gasoline,jet fuel, kerosene and/or diesel produced for example by theFischer-Tropsch (F-T) process), and/or olefins etc.

Existing technologies focus primarily on stand-alone reverse Water GasShift (rWGS) processes to convert CO₂ and H₂ to synthesis gas. Thesynthesis gas can subsequently be converted to valuable products in thedownstream processes as outlined above. The reverse water gas shiftreaction proceeds according to the following reaction:

CO₂+H₂↔HCO+H₂O  (1)

The rWGS reaction (1) is an endothermic process which requiressignificant energy input for the desired conversion. Very hightemperatures are needed to obtain sufficient conversion of carbondioxide into carbon monoxide to make the process economically feasible.Undesired by-product formation of for example methane may also takeplace. High conversions of carbon dioxide can evidently also be obtainedby high H₂/CO₂-ratio. However, this will often result in a synthesis gaswith a (much) too high H₂/CO-ratio for the downstream synthesis.

Technologies relying on the rWGS reaction have other challenges. In somecases, hydrocarbons may be available as co-feed. An example is theavailability of hydrocarbons from a downstream synthesis stage (e.g. apropane and butane rich stream from an F-T stage; tail gas comprisingdifferent hydrocarbons from an F-T stage; naphtha stream from an F-Tstage; propane and butane rich stream from a gasoline synthesis stage; ahydrocarbon stream from olefin synthesis etc.). Such hydrocarbons cannotbe processed in an rWGS reactor. If the hydrocarbon streams from thedownstream synthesis stage are not used at least in part for additionalproduction of synthesis gas, the overall process may not be feasiblefrom an economic point of view. The same is the case if a hydrocarbonstream, such as natural gas, is available as co-feed to the plant.

To address problems with existing technologies, a novel process ofsyngas preparation and then, synthesis from the said syngas to syngasderived product(s) from primarily CO₂, H₂ and O₂ feed is presented inthis document. The proposed layout has at least the followingadvantages:

-   -   1. CO₂, H₂, and O₂ can be converted to syngas with a desired        H₂:CO ratio, suitably without using any hydrocarbon feed to the        plant. If needed, one or more hydrocarbon co-feed to the plant        can be used as well.    -   2. Utilization of any hydrocarbons generated in the synthesis        stage for synthesis gas production    -   3. A higher utilization of the carbon dioxide feed is possible        compared to a stand-alone rWGS section. One particular aim is to        utilize more CO₂ feed instead of hydrocarbon feed as a source of        carbon.    -   4. Conversion of any hydrocarbon co-feed streams fed to the        syngas stage is possible.    -   5. If an electrolyzer is used as part or the entire source of        the hydrogen feed to the process, part or all of the oxygen,        generated in the electrolyzer along with H₂, can be used as the        oxygen source that is required in the proposed process layout.

SUMMARY

In a first aspect, therefore, a method for producing a product stream isprovided. The method comprises the steps of:

-   -   providing a plant, said plant comprising:        -   a. a syngas stage, said syngas stage comprising an            autothermal reforming (ATR) section, and;        -   b. a synthesis stage;            said plant comprising:    -   a first feed comprising hydrogen to the syngas stage;    -   a second feed comprising carbon dioxide to the syngas stage;    -   a third feed comprising hydrocarbons to the syngas stage,        upstream of said ATR section; and    -   a fourth feed comprising oxygen to the ATR section;        wherein said syngas stage is arranged to provide a syngas stream        and feed said syngas stream to the synthesis stage (B);    -   supplying a first feed comprising hydrogen to the syngas stage;    -   supplying a second feed comprising carbon dioxide to the syngas        stage;    -   supplying a third feed comprising hydrocarbons to the syngas        stage, upstream of said ATR section;    -   supplying a fourth feed comprising oxygen to the ATR section;    -   providing a syngas stream in said syngas stage from at least        said first, second, third and fourth feeds, and feeding said        syngas stream to the synthesis stage;    -   converting said syngas stream into at least a product stream and        a hydrocarbon-containing off-gas stream in said synthesis stage;        wherein the ratio of moles of carbon in the third feed        comprising hydrocarbons, when external to the plant, to the        moles of carbon in CO₂ in the second feed is less than 0.5.

Various plants are provided for carrying out the method of theinvention.

Further details of the plant and the method are specified in thefollowing detailed descriptions, figures and claims.

FIGURE LEGENDS

FIGS. 1-5 illustrate schematic layouts of various embodiments of aplant.

DETAILED DISCLOSURE

Unless otherwise specified, any given percentages for gas content are %by volume.

SPECIFIC EMBODIMENTS

As set out above, a plant—such as—a hydrocarbon plant is provided. Theplant comprises:

-   -   a. a syngas stage, said syngas stage comprising an autothermal        reformer (ATR) section, and;    -   b. a synthesis stage;

The plant comprises various feeds. For the avoidance of doubt, the term“feed” when applied to a plant refers to means for supplying said gas tothe appropriate stage, reactor or unit; such as a duct, tubing etc.

A first feed comprising hydrogen is provided to the syngas stage.Suitably, the first feed consists essentially of hydrogen. The firstfeed of hydrogen is suitably “hydrogen rich” meaning that the majorportion of this feed is hydrogen; i.e. over 75%, such as over 85%,preferably over 90%, more preferably over 95%, even more preferably over99% of this feed is hydrogen. One source of the first feed of hydrogencan be one or more electrolyser units. In addition to hydrogen the firstfeed may for example comprise steam, nitrogen, argon, carbon monoxide,carbon dioxide, and/or hydrocarbons. The first feed suitably comprisesonly low amounts of hydrocarbon, such as for example less than 5%hydrocarbons or less than 3% hydrocarbons or less than 1% hydrocarbons.

A second feed comprising carbon dioxide is provided to the syngas stage.Suitably, the second feed consists essentially of CO₂. The second feedof CO₂ is suitably “CO₂ rich” meaning that the major portion of thisfeed is CO₂; i.e. over 75%, such as over 85%, preferably over 90%, morepreferably over 95%, even more preferably over 99% of this feed is CO₂.One source of the second feed of carbon dioxide can be one or moreexhaust stream(s) from one or more chemical plant(s). One source of thesecond feed of carbon dioxide can also be carbon dioxide captured fromone or more process stream(s) or atmospheric air. Another source of thesecond feed could be CO₂ captured or recovered from the flue gas forexample from fired heaters, steam reformers, and/or power plants. Thesecond feed may in addition to CO₂ comprise for example steam, oxygen,nitrogen, oxygenates, amines, ammonia, carbon monoxide, and/orhydrocarbons. The second feed suitably comprises only low amounts ofhydrocarbon, such as for example less than 5% hydrocarbons or less than3% hydrocarbons or less than 1% hydrocarbons.

The first and second feeds could be mixed before being added to thesyngas stage.

The ratio of H₂:CO₂ provided at the plant inlet varies from 1.0-9.0,preferably 2.5-8, more preferably 3.0-7.0. The actual ratio will dependupon the desired end product downstream the synthesis stage. This ratiois defined as any H₂ and CO₂ in external streams (i.e. not includinghydrogen and/or carbon dioxide in any recycle streams).

When the synthesis stage is an FT synthesis stage, the desiredH₂/CO-ratio of the synthesis gas will typically be around 2. Using asimplistic view, one unit of hydrogen is needed to convert each unit ofCO₂ into CO. The addition of O₂ will also require some hydrogen andfurthermore hydrogen will be needed as source of energy for auxiliarypurposes such as for example generation of power. All in all, this meansthat for an FT synthesis stage the H₂:CO₂-ratio at the plant inlet (i.e.not including hydrogen and/or carbon dioxide in any recycle streams)should be in the range of 3-7 or more preferably from 3-6 and mostpreferably 3-5. If the desired end product is methanol or gasoline (viasynthesis of methanol and the methanol-to-gasoline route) a similarconsideration can be made and also in these cases the H₂:CO₂-ratio atthe plant inlet should be in the range of 3-7 or more preferably from3-6 and most preferably 3-5.

It should be noted that in some cases H₂:CO₂ ratios less than 3 such asbetween 2-3 can be utilized. This could for example be the case if thethird stream comprises hydrogen or the third stream is steam reformed toproduce hydrogen. However, other scenarios with an H₂:CO₂ ratios lowerthan 3 are also conceivable.

A third feed comprising hydrocarbons is provided to the syngas stage,upstream of the ATR section. The third feed may additionally compriseother components such as CO₂ and/or CO and/or H₂ and/or steam and/orother components such as nitrogen and/or argon. Suitably, the third feedconsists essentially of hydrocarbons. The third feed of hydrocarbons issuitably “hydrocarbon rich” meaning that the major portion of this feedis hydrocarbons; i.e. over 50%, e.g. over 75%, such as over 85%,preferably over 90%, more preferably over 95%, even more preferably over99% of this feed is hydrocarbons. The concentration of hydrocarbons inthis third feed is determined prior to steam addition (i.e. determinedas “dry concentration”).

In one aspect, the third feed is fed to the syngas stage, directlyupstream of said ATR section (i.e. without any intervening stage orunit). A “stage” comprises one or more “units” which perform a change inthe chemical composition of a feed, and may additionally compriseelements such as e.g. heat exchanger, mixer or compressor, which do notchange the chemical composition of a feed or stream.

An example of such third feed can also be a natural gas stream externalto the plant. In one aspect, said third feed comprises one or morehydrocarbons selected from methane, ethane, propane or butanes.

The source of the third stream comprising hydrocarbons is external tothe plant. The significance of a stream “external to the plant” is thatthe origin of the stream is not a recycle stream (or a recycle streamfurther processed or converted) from any synthesis stage in the plant.Possible sources of a third feed comprising hydrocarbons external to theplant include natural gas, LPG, refinery off-gas, naphtha, andrenewables, but other options are also conceivable.

In some cases, a stream comprising hydrocarbons may be subjected toprereforming before being provided to the syngas stage as the thirdfeed. For example, when the third feed is e.g. a LPG and/or a naphthaproduct stream or a natural gas feed, the plant may further comprise apre-reforming section, arranged in the third feed, upstream the syngasstage.

In a prereforming step, the following (endothermic) steam reformingreaction and reaction (3) (exothermic) take place to convert higherhydrocarbons. Additional water gas shift and methanation takes placethrough reactions (1) and (3):

C_(n)H_(m) +nH₂O↔nCO+(n+m/2)H₂ (where n≥2, m≥4).  (2)

CO₂+4H₂↔CH₄+2H₂O  (3)

The prereformer outlet stream will comprise CO₂, CH₄, H₂O, and H₂ alongwith typically lower quantities of CO and possible other components. Theprereforming step typically takes place at 350-600° C. or morepreferably between 400 and 550° C. Steam is added to the hydrocarbonfeed stream upstream the prereforming step. The prereforming step maytake place either adiabatically or in a heated reactor, filled withcatalysts including but not limited to Ni-based catalysts. Heating ofthe prereformer can be achieved by means of hot gas (e.g. ATR effluentgas) or in a heating section for example using a fired heater. Hydrogenor other combustible components may be used to obtain the necessary heatinput.

A hydrocarbon stream may also contain olefins. In this case the olefinsmay be subjected to hydrogenation to the corresponding paraffins beforeaddition to a prereformer or the syngas stage as the third feed.

In some cases, the hydrocarbons contain minor amount of poisons, such assulfur. In this case, the hydrocarbons may be subjected to the step orsteps of purification such as desulfurization.

The third feed may comprise one or more streams comprising hydrocarbonsthat are either mixed or added separately to the syngas stage. Thestreams comprising hydrocarbons may either be recycled from thesynthesis stage or be one or more separate streams external to the plantand not recycled from the synthesis stage.

A fourth feed comprising oxygen is provided to the ATR section.Suitably, the fourth feed consists essentially of oxygen. The fourthfeed of O₂ is suitably “O₂ rich” meaning that the major portion of thisfeed is O₂; i.e. over 75% such as over 90% or over 95%, such as over 99%of this feed is O₂. This fourth feed may also comprise other componentssuch as nitrogen, argon, CO₂, and/or steam. This fourth feed willtypically include a minor amount of steam (e.g. 5-10%). The source offourth feed, oxygen, can be at least one air separation unit (ASU)and/or at least one membrane unit. The source of oxygen can also be atleast one electrolyser unit. A part or all of the first feed, and a partor all of the fourth feed may come from at least one electrolyser. Anelectrolyser means a unit for converting steam or water into hydrogenand oxygen by use of electrical energy. Steam may be added to the fourthfeed comprising oxygen, upstream the ATR section

In one aspect, the plant further comprises a steam feed (a fifth feed)to the syngas stage.

Suitably, the ratio of moles of carbon in the third feed comprisinghydrocarbons, when external to the plant, to the moles of carbon in CO₂in the second feed is low; such as less than 0.3, preferably less than0.25 and more preferably less than 0.2 or even lower than 0.1. A valueof this ratio less than 0.05 or 0.02 may also be considered. The lowerthe value, the lower the consumption of fossil fuels for a givenproduction in the cases where the external hydrocarbon stream is afossil fuel stream.

Syngas Stage

The syngas stage (A) is arranged to provide a syngas stream (from atleast said first to fourth feeds) and feed said syngas stream to thesynthesis stage (B). For the avoidance of doubt, the terms “syngas” and“synthesis gas” are synonymous. Furthermore, the term “provide a syngasstream” in this context must be understood as to “produce a syngasstream”.

The syngas stage comprises an autothermal reformer (ATR) section. Thesyngas stage may comprise additional sections as required. Varioussections will be described in the following.

ATR Section

In one aspect, the syngas stage consists of said autothermal reforming(ATR) section, comprising one or more autothermal reactors (ATR), andwherein first, second, third, and fourth feeds are fed to said ATRsection. Part or all of the third feed may be desulfurized andprereformed. All feeds are preheated as required. The key part of theATR section is the ATR reactor. The ATR reactor typically comprises aburner, a combustion chamber, and a catalyst bed contained within arefractory lined pressure shell. In an ATR reactor, partial combustionof the hydrocarbon containing feed by sub-stoichiometric amounts ofoxygen is followed by steam reforming of the partially combustedhydrocarbon feed stream in a fixed bed of steam reforming catalyst.Steam reforming also takes place to some extent in the combustionchamber due to the high temperature. The steam reforming reaction isaccompanied by the water gas shift reaction. Typically, the gas is at orclose to equilibrium at the outlet of the reactor with respect to steamreforming and water gas shift reactions. More details of ATR and a fulldescription can be found in the art such as “Studies in Surface Scienceand Catalysis, Vol. 152,” Synthesis gas production for FT synthesis“;Chapter 4, p. 258-352, 2004”.

Typically, the effluent gas from the ATR reactor has a temperature of900-1100° C. The effluent gas normally comprises H₂, CO, CO₂, and steam.Other components such as methane, nitrogen, and argon may also bepresent often in minor amounts. The operating pressure of the ATRreactor will be between 5 and 100 bars or more preferably between 15 and60 bars.

The syngas stream from the ATR is cooled in a cooling train normallycomprising a waste heat boiler(s) (WHB) and one or more additional heatexchangers. The cooling medium in the WHB is (boiler feed) water whichis evaporated to steam. The syngas stream is further cooled to below thedew point for example by preheating the utilities and/or partialpreheating of one or more feed streams and cooling in air cooler and/orwater cooler. Condensed H₂O is taken out as process condensate in aseparator to provide a syngas stream with low H₂O content, which is sentto the synthesis stage.

The “ATR section” may be a partial oxidation “PDX” section. A PDXsection is similar to an ATR section except for the fact that the ATRreactor is replaced by a PDX reactor. The PDX rector generally comprisesa burner and a combustion chamber contained in a refractory linedpressure shell.

The ATR section could also be a catalytic partial oxidation (cPDX)section.

Methanation Section

In one aspect, the syngas stage additionally comprises a methanationsection arranged upstream the ATR section. The methanation section is influid connection with said ATR section. A part or all of the first feedis fed to the methanation section; a part or all of the second feed isfed to the methanation section; and a part or all of the third feed isfed to the syngas stage, upstream said methanation section and/orbetween said methanation section and said ATR section.

The heat generated in the methanation process obviates completely orreduces significantly the need for external preheating of the feed tothe autothermal reforming section. Such external preheating may forexample take place in a fired heater. The required heat in such a firedheater is generated by combustion of for example hydrogen and/or ahydrocarbon. In the former case this consumes part of the feed and inthe second case this leads to CO₂ emissions. Furthermore, a fired heateris an expensive piece of equipment which may also take up a considerableplot area. Finally, the methanation section upfront the ATR sectionimproves the overall plant efficiency for example compared to astand-alone ATR section.

As indicated earlier, state of art for producing a synthesis gas fromCO₂ and hydrogen is based on selective RWGS. Compared to this scheme,the combination of methanation and ATR has several advantages. Thisincludes the possibility of utilizing a hydrocarbon containing streamboth external to the plant and internal recycle streams. Furthermore,the outlet temperature from the ATR reactor in the ATR section willtypically be in the range of 900-1100° C. This is in most cases higherthan is possible with a stand-alone RWGS unit. This increases theproduction of carbon monoxide as tis is thermodynamically favoured byhigher temperature. It should also be noted that even if methane isformed in the methanation section, the content of methane in the finalsynthesis gas sent to the synthesis stage is low due to the high exittemperature from the ATR reaction in the ATR section. Advantageously,the exit temperature from the ATR is between 1000-1100° C.

It is an advantage for most applications that the content of methane inthe synthesis gas sent to the synthesis stage is low. For most types ofsynthesis stages, methane is an inert or even a synthesis stagebyproduct. Hence, in one preferred embodiment, the content of methane inthe synthesis gas sent to the synthesis stage is less than 5%, such asless than 3% or even less than 2%.

It seems counterintuitive to insert a methanation section upstream anATR section. In the methanation section methane is formed and a largepart of the formed methane is then converted in the ATR section.However, the applicants have found that the heat of methanation can beutilized for preheating the feed to the ATR section. This avoids orreduces the need for a dedicated feed preheater. Reducing the preheatduty will also reduce the required combustion to provide the requiredenergy and thereby the emissions of CO₂ in case the preheater is a firedheater with hydrocarbon fuel. The methanation section may comprise oneor more methanation units, arranged in series, such as two or moremethanation units, three or more methanation units, four or moremethanation units. In such methanation units, CO₂ and H₂ are primarilyconverted to methane and steam via an exothermic methanation reaction.Each of the methanation units may be either adiabatic or cooled by meansfor example of boiling water or by heating for example the feed gas. Theeffluent temperature from each methanation unit can be 250-900° C.,preferably 600-850° C., more preferably 650-840° C., depending on theextent of methanation and extent of cooling. Parallel methanation unitsare also conceivable.

Parts of the first feed comprising hydrogen may be fed separately todifferent methanation units in the methanation section; or the entirefirst feed comprising hydrogen may be fed together to the methanationunit located furthest upstream in the methanation section. Similarly,parts of the second feed comprising carbon dioxide may be fed separatelyto different methanation units in the methanation section; or the entiresecond feed comprising carbon dioxide may be fed together to themethanation unit located furthest upstream in the methanation section.Furthermore, parts of the third feed comprising hydrocarbons may be fedseparately to different methanation units in the methanation section; orthe entire third feed comprising hydrocarbons may be fed together to onemethanation unit in the methanation section.

In a specific embodiment, all of the first feed comprising hydrogen isfed to the first of the methanation units together with part of thesecond feed comprising carbon dioxide. The remaining part of the carbondioxide is distributed between the remaining methanation units and theexit temperature of the final methanation unit is between 650-900° C.such as between 750-850° C.

Additional H₂ feed and/or CO₂ feed can be added to different parts ofthe methanation section. For instance, part of the hydrogen or CO₂ feedcould be provided to a second (or even third . . . ) methanation unit.Additionally, part of the effluent from one methanation unit can becooled and recycled to the inlet of said methanation unit and/or to theinlet of any additional methanation unit(s) located upstream said onemethanation unit. Optionally, effluent from methanation section can becooled below its dew point and a part of the water may be removed fromthis effluent before it is recycled to the inlet of the methanation unitor any upstream methanation unit.

Addition of steam to the methanation section and/or between themethanation section and the ATR section may also occur.

In this aspect, the exothermic nature of the methanation reaction may beutilized for preheating the ATR feed. Some heating of the ATR section byexternal means may be either needed or desirable for example for controlpurposes. Therefore, the reaction heat of the methanation reaction mayonly cause part of the temperature increase upstream the ATR section.

The methanation reaction can be expressed by:

CO₂+4H₂↔CH₄+2H₂O  (3)

Normally, the rWGS (reaction (1) and/or the water gas shift reaction(reverse of reaction (1)) will also take place in the methanation unit.In many cases, the gas composition at the exit of each methanation unitwill be at or close to chemical equilibrium with respect to the watergas shift/reverse water gas shift and the methanation reactions at theexit temperature and pressure of said methanation unit.

The methanation reaction (3) is very exothermic. In some cases, it isdesirable to adjust the temperature at the outlet of a methanation unitor from the methanation section to a given value, which may be in therange of 250-900° C. such as between 600-850° C. If part or all of thethird feed comprising hydrocarbons is added to a methanation unit, thiswill reduce the exit temperature due to the fact that steam reforming(reverse of reaction (3) and/or reaction (2)) will take place.

If instead, the effluent from the prereforming step is added to amethanation unit, the same effect will be obtained. The methane in theprereforming effluent will react according to the endothermic steamreforming reaction:

CH₄+H₂O↔CO+3H₂  (4)

The presence of methane in the feed will limit the extent of themethanation reaction due to the chemical equilibrium. The output fromthe methanation section is a stream comprising CO₂, H₂, CO, H₂O and CH₄.

A tail gas from an FT synthesis stage will normally not be added to amethanation unit but fed directly to the ATR section. If excess tail gasfrom the FT synthesis stage is available, this may be hydrogenated andfed to the methanation section.

In some cases, it may be desirable to avoid to too high temperatures inthe methanation unit for example to limit the extent of deactivation ofthe catalyst due to sintering. This is especially the case if themethanation unit or methanation reactor is adiabatic. The highesttemperature in an adiabatic methanation unit will normally be at theoutlet. Hence, it may be desirable to control the exit temperature fromone or more methanation units to for example a temperature in the range600-750° C., such as about 650° C., 675° C., 700° C., or 725° C. Thismay be accomplished by controlling the feed streams to the individualmethanation units in the methanation section, if more than onemethanation unit is present. By controlling the molar ratios between thepart of the first feed and the part of the second feed as well as themolar ratio between the part of the first feed and the part of the fifthfeed (if present) added to a methanation unit, it is possible to controlthe exit temperature of an adiabatic methanation unit. Obviously, theinlet temperature(s) of the feed streams can also be used for thispurpose.

In one embodiment, the inlet temperature of at least one of themethanation units will be between 300-500° C.

The control of the ratios of the various feed streams to each of themethanation units and the ratios of the various feed streams fed to themethanation section and directly to the ATR section may also be used toimpact the synthesis gas composition.

The extent of methanation (and thereby the composition of the gas to theATR section) depends on a number of factors including the ratio of thefeed streams to the methanation section and the inlet and exittemperature to and from each methanation unit and the extent of waterremoval (if any) from the methanation section. For a given gascomposition and temperature of the gas to the ATR section, the synthesisgas from the ATR depends upon the amount of oxygen added. Increasing theamount of oxygen increases the ATR reactor exit temperature and therebyreduces the H₂/CO-ratio.

In another embodiment (illustrated in FIG. 4c ) the syngas stage (A)comprises a methanation section (II) arranged in parallel to said ATRsection (I). At least a portion of the first feed and at least a portionof the second feed are arranged to be fed to the methanation section(II) and said methanation section (II) is arranged to convert said atleast a portion of the first feed and at least a portion of the secondfeed to a first syngas stream. A third feed comprising hydrocarbons anda fourth feed comprising oxygen are arranged to be fed to the ATRsection (I); and wherein said ATR section (I) is arranged to convertsaid third feed comprising hydrocarbons and said fourth feed comprisingoxygen along with the remaining portions of the first and second streamsto a second syngas stream. The first syngas stream from the methanationsection (II) is arranged to be combined with the second syngas streamfrom the ATR section (I); and the combined syngas stream is arranged tobe fed to the synthesis stage (B).

Compared to in series methanation and ATR section, this embodimentreduces the amount of oxygen needed.

Reverse Water Gas Shift (rWGS) Section

In a further aspect, the syngas stage comprises a reverse water gasshift (rWGS) section upstream the ATR section. The reverse water gasshift (rWGS) section is in fluid connection with said ATR section. Apart or all of the first feed is fed to the rWGS section; a part or allof the second feed is fed to the rWGS section; and wherein a part orpreferably all of the third feed may be fed to the syngas stage betweensaid rWGS section (III) and said ATR section.

As indicated earlier, state of art for producing a synthesis gas fromCO₂ and hydrogen is based on selective RWGS. Compared to this scheme,the combination of RWGS and ATR has several advantages. This includesthe possibility of utilizing a hydrocarbon containing stream bothexternal to the plant and internal recycle streams. Such streams can beadded to the ATR section and utilized for additional synthesis gasproduction compared to what is possible with a stand-alone and selectiveRWGS. Furthermore, the outlet temperature from the ATR reactor in theATR section will typically be in the range of 900-1100° C. This is inmost cases higher than is possible with a stand-alone RWGS unit. Thisincreases the production of carbon monoxide as this is thermodynamicallyfavoured by higher temperature.

In one aspect, the rWGS section comprises one or more rWHS units,arranged in series e.g. two or more rWGS units, such as three or morerWGS units. In such rWGS units, CO₂ and H₂ are converted to CO and H₂via reaction (1) above. Parallel reverse water gas shift units are alsoconceivable.

Parts of the first feed comprising hydrogen may be fed separately todifferent rWGS units in the rWGS section; or the entire first feedcomprising hydrogen is fed together to the reverse WGS unit locatedfurthest upstream in the rWGS section. Similarly, parts of the secondfeed comprising carbon dioxide may be fed separately to different rWGSunits in the rWGS section; or the entire second feed comprising carbondioxide is fed all together to the rWGS unit located furthest upstreamin the rWGS section.

Each of the rWGS units may be either adiabatic or a heated reactor.Heating can be achieved by means of hot effluent from ATR or utilizingheat of combustion of, for example—a stream comprising hydrocarbonsand/or a stream comprising hydrogen. The effluent from the rWGS sectionis a stream comprising CO₂, H₂, CO, H₂O. The rWGS effluent temperaturefrom each rWGS unit can be 400-900° C., preferably 500-900° C., morepreferably 500-750° C., depending on the extent of rWGS and extent ofheating.

The effluent from the rWGS section is fed to the ATR section. Amethanation section, in one specific embodiment, may be placed betweenthe rWGS section and the ATR section. In this case the effluent from therWGS section is fed to the methanation section and the effluent from themethanation section is fed to the ATR.

Reverse Water Gas Shift (rWGS) Section—Alternative Arrangement

In a further aspect, the syngas stage comprises a reverse water gasshift (rWGS) section which is arranged in parallel to said ATR section.The reverse water gas shift (rWGS) section is in fluid connection withsaid ATR section. A part or all of the first feed is fed to the rWGSsection; a part or all of the second feed is fed to the rWGS section;wherein the said rWGS section is arranged to convert at least a portionof the first feed and at least a portion of the second feed to a syngasstream comprising H₂, CO, CO₂ and H₂O.

Third feed comprising hydrocarbons and a fourth feed comprising oxygenalong with optionally a portion of first feed comprising hydrogen and/oroptionally a portion of second feed comprising carbon dioxide arearranged to feed to the ATR section; wherein the ATR section is arrangedto convert the feed streams to another syngas stream comprising H₂, CO,CO₂, CH₄ and H₂O.

In this aspect, syngas streams from the rWGS section and the ATR sectionare arranged to be combined to obtain a final syngas stream; wherein thesaid final syngas stream is fed to synthesis stage.

As indicated earlier, state of art for producing a synthesis gas fromCO₂ and hydrogen is based on selective RWGS. Compared to this scheme,the combination of a parallel RWGS and ATR has several advantages. Thisincludes the possibility of utilizing a hydrocarbon containing streamboth external to the plant and internal recycle streams. Converting partof the CO₂ in the RWGS section has the advantage that the overall oxygenconsumption may be reduced.

As above, this rWGS section may comprise one or more rWHS units,arranged in series e.g. two or more rWGS units, such as three or morerWGS units. In such rWGS units, CO₂ and H₂ are converted to CO and H₂via reaction (1) above. Parallel reverse water gas shift units are alsoconceivable.

Parts of the first feed comprising hydrogen may be fed separately todifferent rWGS units in the rWGS section; or the entire first feedcomprising hydrogen is fed together to the reverse WGS unit locatedfurthest upstream in the rWGS section. Similarly, parts of the secondfeed comprising carbon dioxide may be fed separately to different rWGSunits in the rWGS section; or the entire second feed comprising carbondioxide is fed all together to the rWGS unit located furthest upstreamin the rWGS section.

Each of the rWGS units may be either adiabatic or a heated reactor.Heating can be achieved by means of hot effluent from ATR or utilizingheat of combustion of, for example—a stream comprising hydrocarbonsand/or a stream comprising hydrogen. The effluent from the rWGS sectionis a stream comprising CO₂, H₂, CO, H₂O. The rWGS effluent temperaturefrom each rWGS unit can be 400-900° C., preferably 500-900° C., morepreferably 500-750° C., depending on the extent of rWGS and extent ofheating.

Post ATR CO₂-Conversion Unit

In another aspect, the plant comprises a post-conversion (post-ATRconversion, PAC) unit or reactor, located downstream the ATR section.

The PAC unit may be either adiabatic or a heated reactor using forexample a Ni-based catalyst and/or a catalyst with noble metals such asRu, Rh, Pd, and/or Ir as the active material. In such a PAC unit, astream comprising carbon dioxide such as part of the second feed andpart or all of the syngas from the ATR section is mixed and directed tothe PAC unit. The mixed stream is converted to a syngas with highercarbon monoxide content via both reactions (3) and (1) above in the PACunit. Reactions (3) and (1) will typically be at or close to chemicalequilibrium at the outlet of the PAC unit. The effluent from the PACsection is a stream comprising CO₂, H₂, CO, H₂O and CH₄. The PACeffluent temperature from each PAC unit can be 700-1000° C., preferably800-950° C., more preferably 850-920° C. The advantage of the PAC unitis the ability to produce a synthesis gas a lower H₂/CO-ratio comparedto the effluent stream from the ATR section. Furthermore, the fact thata stream comprising carbon dioxide such as part of the second feed isdirected to the PAC unit (such as an adiabatic PAC unit) instead of tothe ATR section, reduces the size of the ATR section.

This may in some cases reduce the overall cost.

The effluent stream from the PAC unit is cooled as described above toprovide a syngas stream for the synthesis stage.

This CO₂-conversion (PAC) unit may be included in any of the aspectsdescribed above.

Synthesis Stage

The synthesis stage is typically arranged to convert the syngas streaminto at least a product stream.

Often a hydrocarbon-containing off-gas stream is generated in thesynthesis stage. Suitably, at least a portion of saidhydrocarbon-containing off-gas stream is fed to the syngas stage inaddition to said third feed comprising hydrocarbons.

A few examples (not exhaustive) of possible off-gas streams to be fed tothe syngas stage in addition to the third feed comprising hydrocarbons;and corresponding synthesis stages are provided in the following table.

Possible off-gas streams Synthesis stage technology from synthesis stageFischer-Tropsch (F-T) Tail gas Propane/butane rich stream (LPG) Naphtharich stream Methanol (MeOH) synthesis Purge gas MeOH to gasoline (MTG)Purge gas Propane/butane rich stream (LPG) Higher alcohol synthesis (HA)Tail gas Methane rich stream Syngas-to-Olefin (STO) synthesis CO₂-richoff gas Hydrocarbon rich stream

In the case where off-gas stream is fed to the syngas stage in additionto the third feed comprising hydrocarbons, the requirement for anexternal hydrocarbon feed may be reduced.

The syngas stream at the inlet of said synthesis stage suitably has aH₂:CO ratio in the range 1.00-4.00; preferably 1.50-3.00, morepreferably 1.50-2.10. If the synthesis stage is an FT stage, the H₂:COratio is preferably in the range 1.50-2.10.

In another embodiment, the syngas stream at the inlet of said synthesisstage suitably has a (H₂−CO₂)/(CO+CO₂) ratio in the range 1.50-2.50;preferably 1.80-2.30, more preferably 1.90-2.20. This stoichiometry issuitable for methanol synthesis.

The present technology and the composition of syngas can be applied to avariety of syntheses and synthesis stages. A few potential examples ofthe synthesis stage are provided in the following.

Fischer-Tropsch Synthesis Stage

In one aspect, the synthesis stage is a Fischer-Tropsch synthesis (F-T)stage. The F-T stage comprises Fischer-Tropsch (F-T) synthesis sectionwhere syngas from syngas stage is first converted to at least a rawproduct comprising hydrocarbons and a hydrocarbon containing off-gasstream in form of an F-T tail gas stream followed by hydroprocessing andhydrocracking section where said raw product is converted to at leastone or more hydrocarbon product streams. The composition of the rawproduct from the F-T synthesis section depends on the type of catalyst,reaction temperature etc. that are used in the process.

A hydrocarbon-containing off-gas stream in the form of an F-T tail gasstream is produced as side-product. The F-T tail gas stream typicallycomprises carbon monoxide (10-40 vol. %), hydrogen (10-40 vol %), carbondioxide (10-50 vol %), and methane (10-40 vol %). Additional componentssuch as argon, nitrogen, olefins, and paraffins with two or more carbonatoms may also be present in smaller amounts.

At least a portion of said F-T tail gas stream may be fed to the syngasstage in addition to said third feed comprising hydrocarbons. Suitably,to avoid excessive build-up of inert components, that may be present inF-T tail gas, only a portion of said F-T tail gas stream is fed to thesyngas stage; and another portion of the F-T tail gas may be purgedand/or used as fuel and/or converted to power. In one embodiment saidpower can be used as (partial) source for an electrolysis unit ifpresent. Alternatively, the power can be exported.

In one embodiment, the major product from F-T synthesis stage is/aretypically jet fuel and/or kerosene (e.g. comprising primarily C₁₂-C₁₅)and/or diesel (e.g. comprising primarily C₁₅-C₂₀). Besides, naphtha(e.g. comprising primarily C₅-C₁₂) and LPG (e.g. comprising primarilyC₃-C₄) streams are also produced in F-T synthesis stage. A part or allof such LPG and/or naphtha stream(s) from F-T synthesis stage may alsobe used additional to the third feed comprising hydrocarbons to syngasstage. A part or all of such LPG and/or naphtha stream(s) may be addedto the methanation section and/or directly to the ATR section. Inanother embodiment, a part or all of such LPG and/or naphtha may besubjected to prereforming section before addition to the methanationsection and/or the ATR section.

In one particular embodiment, therefore, the synthesis stage is aFischer-Tropsch synthesis (F-T) stage arranged to convert said syngasstream from said syngas stage into at least a hydrocarbon productstream, being a diesel stream; and an LPG and/or a naphtha productstream and/or kerosene or jet fuel product stream, and wherein at leasta portion of said LPG and/or a naphtha product stream is fed to thesyngas stage in addition to said third feed comprising hydrocarbons. Inone aspect, at least a portion of the FT tail gas, at least a portion ofthe LPG and at least a portion of the naphtha product stream are fed tothe syngas stage. In another aspect, at least a portion of the FT tailgas and at least a portion of the LPG are fed to the syngas stage. TheLPG and/or naphtha stream(s) may be treated by prereforming before beingfed to the syngas stage.

Methanol Synthesis Stage

In another embodiment, the synthesis stage is a methanol (MeOH)synthesis stage. This stage comprises a MeOH synthesis section wheresyngas from the syngas stage is first converted to a raw MeOH stream,followed by a purification section where said raw MeOH stream ispurified to obtain a MeOH product stream. The MeOH synthesis stagegenerates a purge gas stream, which typically contains hydrogen, carbondioxide, carbon monoxide and methane. Additional components such asargon, nitrogen, or oxygenates with two or more carbon atoms may also bepresent in smaller amounts.

At least a portion of said MeOH purge gas stream may be fed to thesyngas stage in addition to said third feed comprising hydrocarbons. TheMeOH purge gas stream may be purified prior to feeding it to the syngasstage. Suitably, to avoid excessive build-up of inert components thatmay be present in the MeOH purge gas, only a portion of said MeOH purgegas stream may be fed to the syngas stage; and another portion of theMeOH purge gas may be purged and/or used as fuel.

In particular when the synthesis stage is a methanol synthesis stage,the syngas stream at the outlet of said syngas stage has a module, asdefined herein, in the range 1.80-2.30; preferably 1.90-2.20. The term“module” is defined as:

${Module},{M = \frac{\left( {H_{2} - {CO}_{2}} \right)}{\left( {{CO} + {CO}_{2}} \right)}}$

Methanol-to-Gasoline (MTG) Synthesis Stage

In another embodiment, the synthesis stage is a MeOH-to-gasoline (MTG)synthesis stage comprising a MeOH synthesis section where syngas fromsyngas stage is first converted to raw MeOH stream followed by agasoline synthesis section where said raw MeOH stream is converted togasoline product stream.

The MTG synthesis stage also generates a purge gas stream. This purgegas stream can be utilized similarly as explained in the previoussection under ‘Methanol synthesis stage’.

The MTG synthesis stage generates LPG (e.g. comprising primarily C₃-C₄)stream. A part or all of such LPG stream from MTG synthesis stage mayalso be fed additional to the said third feed comprising hydrocarbons tothe syngas stage. A part or this entire LPG stream may be added to themethanation section and/or directly to the ATR section. In anotherembodiment, a part or all of said LPG stream may be subjected toprereforming before addition to the methanation section and/or the ATRsection.

Higher Alcohol (HA) Synthesis

In another embodiment, the synthesis stage is a higher alcohol (HA)synthesis stage comprising HA synthesis section where syngas from syngasstage is first converted to raw alcohol stream followed by purificationsection where said raw alcohol stream is purified to get HA productstream.

HA synthesis stage may generate a tail gas stream, which typicallycontains hydrogen, carbon dioxide, carbon monoxide. Additionalcomponents such as argon, nitrogen, methane, oxygenates with two or morecarbon atoms may also be present in smaller amounts.

HA synthesis stage may also generate a methane rich stream, whichtypically contains methane, hydrogen and carbon monoxide. Additionalcomponents such as argon, nitrogen, carbon dioxide, oxygenates with twoor more carbon atoms may also be present in smaller amounts.

At least a portion of said tail gas and/or said methane rich stream(s)may be fed to the syngas stage in addition to said third feed comprisinghydrocarbons. Suitably, to avoid excessive build-up of inert components,that may present in said tail gas and/or said methane rich stream(s),only a portion of said tail gas and/or said methane rich stream(s) maybe fed to the syngas stage; and the another portion may be purged and/orused as fuel.

Syngas-to-Olefins (STO) Synthesis

In another embodiment, the synthesis stage is a syngas-to-olefins (STO)synthesis stage comprising STO synthesis section where syngas fromsyngas stage is first converted to raw olefin rich stream followed bypurification section where said raw olefin rich stream is purified toget olefin product stream.

STO synthesis stage may generate a tail gas stream, which typicallycontains hydrogen, carbon dioxide, carbon monoxide. Additionalcomponents such as argon, nitrogen, methane, hydrocarbons with two ormore carbon atoms may also be present in smaller amounts.

STO synthesis stage may also generate a hydrocarbon rich stream, whichtypically contains methane and higher hydrocarbons with two or morecarbon atoms. Higher hydrocarbons may be both olefins and paraffins.Additional components such as hydrogen, carbon dioxide, carbon monoxide,argon, nitrogen may also be present in smaller amounts.

At least a portion of said tail gas and/or said hydrocarbon richstream(s) may be fed to the syngas stage in addition to said third feedcomprising hydrocarbons. Suitably, to avoid excessive build-up of inertcomponents, that may present in said tail gas and/or said hydrocarbonrich stream(s), only a portion of said tail gas and/or said hydrocarbonrich stream(s) may be fed to the syngas stage; and the another portionmay be purged and/or used as fuel.

Syngas-to-Ethylene Oxide (STEtO) Synthesis

In another embodiment, the synthesis stage is a syngas-to-ethylene oxide(STEtO) synthesis stage. The STEtO stage comprises syngas-to-olefin(STO) synthesis section, where syngas is first converted to olefinproduct (mainly ethylene), followed by the ethylene oxide synthesissection.

STO synthesis stage may generate a tail gas stream, which typicallycontains hydrogen, carbon dioxide, carbon monoxide. Additionalcomponents such as argon, nitrogen, methane, hydrocarbons with two ormore carbon atoms may also be present in smaller amounts.

STO synthesis stage may also generate a hydrocarbon rich stream, whichtypically contains methane and higher hydrocarbons with two or morecarbon atoms. Higher hydrocarbons may be both olefins and paraffins.Additional components such as hydrogen, carbon dioxide, carbon monoxide,argon, nitrogen may also be present in smaller amounts.

At least a portion of said tail gas and/or said hydrocarbon richstream(s) may be fed to the syngas stage in addition to said third feedcomprising hydrocarbons. Suitably, to avoid excessive build-up of inertcomponents, that may present in said tail gas and/or said hydrocarbonrich stream(s), only a portion of said tail gas and/or said hydrocarbonrich stream(s) may be fed to the syngas stage; and the another portionmay be purged and/or used as fuel.

The ethylene oxide synthesis section may use at least a part of thefourth feed (O₂). Lots of CO₂ is generated as by-product during ethyleneoxide synthesis. The CO₂ by-product can be recycled and used at least apart of the first feed to syngas stage.

Combined Gasoline and Diesel Production

In another embodiment, synthesis stage can be combination of F-T sectionand methanol-to-gasoline (MTG) synthesis sections in parallel withcommon syngas feed from syngas stage. The F-T section produces middledistillate products (diesel/jet fuel/kerosene etc.), and MTG producesgasoline with desired octane number. In this embodiment, syngas stageprovides syngas of suitable quality to both F-T and MTG sections,operating in parallel to each other. At least a part of recycle gas fromF-T and/or at least a part of LPG stream from MTG section and/or atleast a part of purge stream from MeOH synthesis section can be used asthird feed to syngas stage.

Electrolyzer

The plant may further comprise an electrolyser arranged to convert wateror steam into at least a hydrogen-containing stream and anoxygen-containing stream, wherein at least a part of saidhydrogen-containing stream from the electrolyser is fed to the syngasstage as said first feed and/or wherein at least a part of saidoxygen-containing stream from the electrolyser is fed to the syngasstage as said fourth feed. An electrolyser may comprise one or moreelectrolysis units, for example based on solid oxide electrolysis.

In one preferred embodiment, therefore, the plant further comprises anelectrolyser located upstream the syngas stage. The electrolyser isarranged to convert water or steam into at least a hydrogen-containingstream and an oxygen-containing stream.

At least a part of the hydrogen-containing stream from the electrolyseris fed to the syngas stage as said first feed. Alternatively oradditionally, at least a part of the oxygen-containing stream from theelectrolyser is fed to the syngas stage as said fourth feed. Thisprovides an effective source of the first and fourth feeds.

In a preferred aspect, all of the hydrogen in the first feed and all ofthe oxygen in the fourth feed is produced by electrolysis. In thismanner the hydrogen and the oxygen required by the plant is produced bysteam and electricity. Furthermore, if the electricity is produced onlyby renewable sources, the hydrogen and oxygen in the first and fourthfeed, respectively, are produced without fossil feedstock or fuel.

Preferably, the water or steam fed to the electrolyser is obtained fromone or more units or stages in said plant.

The use of an electrolyser may be combined with any of the describedembodiments in this document.

Additional Aspects

Optionally, the plant may comprise a sixth feed comprising hydrogen tothe syngas stream, upstream the synthesis stage. This sixth feed mayhave the same composition as the first feed comprising hydrogen, i.e.the sixth feed consists essentially of hydrogen, and over 75%, such asover 85%, preferably over 90%, more preferably over 95%, even morepreferably over 99% of this feed may be hydrogen.

The sixth feed can be used to adjust the syngas composition (such as theH₂/CO ratio) in the syngas stream, if required. In a preferred aspect,at least a part of the hydrogen-containing stream from an electrolyseris fed to the syngas stream, upstream the synthesis stage as said sixthfeed of hydrogen. This provides additional opportunities for a systemwhich does not require additional external input of gas and allows finaladjustment of the gas composition upstream the synthesis stage.

The composition of the syngas from the syngas stage can be adjusted inother ways. For instance, the plant may further comprise a hydrogenremoval section, located between said syngas stage and said synthesisstage, arranged to remove at least part of the hydrogen from the syngasstream. In this case, at least a portion of the hydrogen removed fromthe syngas stream in said hydrogen removal section may be compressed andfed as part of said first feed to the syngas stage. Hydrogen removalunits can be, but not limited to, pressure swing adsorption (PSA) unitsor membrane units.

Furthermore, the plant may further comprise a carbon dioxide removalsection, located between said syngas stage and said synthesis stage, andarranged to remove at least part of the carbon dioxide from the syngasstream. In this case, at least a portion of the carbon dioxide removedfrom the syngas stream in said carbon dioxide removal section may becompressed and fed as part of said second feed to the syngas stage.Carbon dioxide removal units can be, but not limited to, an amine-basedunit or a membrane unit.

An off-gas stream may be treated to remove one or more components, or tochange the chemical nature of one or more components, prior to being fedto the syngas stage. The off-gas, for example an F-T tail gas, maycomprise olefins. Olefins increase the risk of carbon deposition and/ormetal dusting at high temperatures. Therefore, the plant may furthercomprise a hydrogenator arranged in the F-T tail gas recycle stream. Thehydrogenator arranged to hydrogenate the third feed, before said thirdfeed enters the syngas stage. In this manner, olefins can effectively beconverted to saturated hydrocarbons before entering the syngas stage.

An off-gas stream or the part of an off-gas stream not recycled to thesynthesis gas stage or used for other purposes may be used to produceadditional synthesis gas in a separate synthesis gas generator. Such asynthesis gas generator may comprise technologies known in the art suchas ATR, steam reforming (SMR), and/or adiabatic prereforming, but alsoother technologies are known. Such additional synthesis gas may be fedto the synthesis stage. As an example, tail gas from a Fischer-Tropschsynthesis stage may be converted into additional synthesis gas by meansknown in the art such as comprising hydrogenation, followed by water gasshift, and autothermal reforming.

Method

A method for producing a product stream is provided, said methodcomprising the steps of:

-   -   providing a plant (X), said plant comprising:        -   a. a syngas stage (A), said syngas stage comprising an            autothermal reforming (ATR) section (I), and;        -   b. a synthesis stage (B);        -   said plant comprising:            -   a first feed (1) comprising hydrogen to the syngas                stage;            -   a second feed (2) comprising carbon dioxide to the                syngas stage;            -   a third feed (3) comprising hydrocarbons to the syngas                stage, upstream of said ATR section; and            -   a fourth feed (4) comprising oxygen to the ATR section;        -   wherein said syngas stage (A) is arranged to provide a            syngas stream (100) and feed said syngas stream (100) to the            synthesis stage (B);    -   supplying a first feed (1) comprising hydrogen to the syngas        stage;    -   supplying a second feed (2) comprising carbon dioxide to the        syngas stage;    -   supplying a third feed (3) comprising hydrocarbons to the syngas        stage, upstream of said ATR section (I);    -   supplying a fourth feed (4) comprising oxygen to the ATR        section;    -   providing a syngas stream (100) in said syngas stage (A) from at        least said first, second, third and fourth feeds, and feeding        said syngas stream (100) to the synthesis stage (B);    -   converting said syngas stream (100) into at least a product        stream (500) and a hydrocarbon-containing off-gas stream (3 b)        in said synthesis stage (B); and    -   optionally, feeding at least a portion of said        hydrocarbon-containing off-gas stream (3 b) to the syngas        stage (I) in addition to said third feed (3) comprising        hydrocarbons; upstream of said ATR section (I);    -   wherein the ratio of moles of carbon in the third feed        comprising hydrocarbons, when external to the plant, to the        moles of carbon in CO₂ in the second feed is less than 0.5.

All aspects relating to the plant set out above are equally applicableto the method using said plant. The term “feed” when applied to themethod of the invention refers to providing a flow of said gas to theappropriate stage, reactor or unit. In particular, the following aspectsof particular importance to the method of the invention are noted:

-   -   the method may comprise the additional step of feeding at least        a portion of said hydrocarbon-containing off-gas stream to the        syngas stage in addition to said third feed comprising        hydrocarbons.    -   the synthesis stage may be a Fischer-Tropsch (F-T) stage        arranged to convert said syngas stream into at least a        hydrocarbon product stream and a hydrocarbon-containing off-gas        stream in the form of an F-T tail gas stream.    -   an electrolyser may be located upstream the syngas stage and the        method may further comprise conversion of water or steam into at        least a hydrogen-containing stream and an oxygen-containing        stream. The method may further comprise the steps of; feeding at        least a part of said hydrogen-containing stream from the        electrolyser to the syngas stage as said first feed of hydrogen        and/or feeding at least a part of said oxygen-containing stream        from the electrolyser to the syngas stage as said fourth feed of        oxygen. The method may further comprise obtaining the water or        steam which is fed to the electrolyser is obtained as condensate        from one or more units or stages in said hydrocarbon plant.    -   the ratio of moles of carbon in the third feed comprising        hydrocarbons, when external to the plant, to the moles of carbon        in CO₂ in the second feed is less than 0.3, preferably less than        0.25 and more preferably less than 0.20 or even lower than 0.10.    -   the syngas stream at the inlet of said synthesis stage has a        hydrogen/carbon monoxide ratio in the range 1.00-4.00;        preferably 1.50-3.00, more preferably 1.50-2.10.    -   the ratio of H₂:CO₂ provided at the plant inlet is between        1.0-9.0, preferably 2.5-8.0, more preferably 3.0-7.0.    -   the synthesis stage is an FT synthesis stage and the        H₂:CO₂-ratio at the plant inlet is in the range of 3.0-7.0 or        more preferably from 3.0-6.0 and most preferably 3.0-5.0.    -   the syngas stage (A) consists of said autothermal reforming        (ATR) section (I), and wherein first, second, third and fourth        feeds are fed to said ATR section.    -   the syngas stage additionally comprises a methanation        section (II) arranged upstream the ATR section (I); wherein a        part or all of the first feed is fed to the methanation section;        a part or all of the second feed is fed to the methanation        section; and wherein a part or all of the third feed is fed to        the syngas stage; upstream said methanation section or between        said methanation section and said ATR section.    -   the syngas stage additionally comprises a reverse water gas        shift (rWGS) section (III) upstream the ATR section (I) wherein        a part or all of the first feed (1 d) is fed to the rWGS        section; a part or all of the second feed is fed to the rWGS        section; and wherein a part or all of the third feed is fed to        the syngas stage between said rWGS section (III) and said ATR        section.    -   the syngas stage (A) comprises a reverse water gas shift (rWGS)        section (III) arranged in parallel to said ATR section (I);        wherein at least a portion of the first feed and at least a        portion of the second feed are arranged to be fed to the rWGS        section and said rWGS section is arranged to convert said at        least a portion of the first feed and at least a portion of the        second feed to a first syngas stream; wherein a third feed        comprising hydrocarbons and a fourth feed comprising oxygen are        arranged to be fed to the ATR section (I); and wherein said ATR        section (I) is arranged to convert said third feed comprising        hydrocarbons and said fourth feed comprising oxygen to a second        syngas stream, wherein the first syngas stream from the rWGS        section (III) is arranged to be combined with the second syngas        stream from the ATR section (I); and the combined syngas stream        is arranged to be fed to the synthesis stage.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a schematic layout of a first embodiment of a plant

-   A syngas stage-   B synthesis stage-   1 first feed (comprising hydrogen) to syngas stage-   2 second feed (comprising carbon dioxide) to syngas stage-   3 third feed (hydrocarbon which can be external to the plant and/or    internal stream) to syngas stage-   4 fourth feed (comprising oxygen) to syngas stage-   100 syngas product from syngas stage-   500 product from synthesis stage

FIG. 1a illustrates a schematic layout of a first embodiment of a plantin which the hydrocarbon feed can be both from external sources or fromthe synthesis stage, e.g. more than one, for example three hydrocarbonstreams from the synthesis stage. Reference numbers are for FIG. 1,plus:

-   3 a a part of third feed from external source (e.g. external    hydrocarbon stream such as natural gas) to syngas stage-   3 b a part of third feed from synthesis stage (e.g. tail gas from    F-T) to syngas stage-   3 c another part of third feed from synthesis stage (e.g. LPG stream    from F-T) to syngas stage-   3 d another part of third feed from synthesis stage (e.g. naphtha    stream from F-T) to syngas stage

FIG. 2 illustrates a schematic layout of another embodiment of a plant,in which the syngas stage comprises a prereforming section (Ia) and anATR section (I), and in which steam as fifth feed (5) is shown.Reference numbers are for FIG. 1 and 1 a, plus:

-   (Ia) prereforming section-   (I) ATR section-   1 a part of first feed to prereforming section-   1 b part of first feed to ATR section-   5 fifth feed (steam)-   10 prereformed hydrocarbon to ATR section

FIG. 3 illustrates a schematic layout of another embodiment of a plant,in which the syngas stage comprises methanation section (II) and ATRsection (I). The effluent from methanation section (II) is sent to ATRsection (I). Reference numbers are as for the previous figures, plus:

-   (II) methanation section-   30 effluent from methanation section to ATR section

FIG. 3a illustrates a variation of the schematic layout, described inFIG. 3. In this embodiment of a plant, hydrocarbon feeds are treated inprereforming section (Ia) before feeding it to methanation section (II)followed by ATR section (I). Fifth feed steam (5) is introduced toprereforming section. Reference numbers are as for the previous figures,plus:

-   20 prereformed hydrocarbon to methanation section

FIG. 3b illustrates a variation of the schematic layout, described inFIG. 3a . This is an embodiment of a plant with a part of the steam (5a) addition to is sent to prereforming section and another part of thesteam (5 b) addition to methanation section. Reference numbers are asfor the previous figures, plus:

-   5 a part of fifth feed to prereforming section-   5 b part of the fifth feed to methanation section

FIG. 4 illustrates a schematic layout of another embodiment of a plant,in which the syngas stage comprises an rWGS section (III) plus an ATRsection (I). Reference numbers are as for the previous figures, plus:

-   (III) rWGS section-   1 d part of first feed to section rWGS section-   40 syngas stream from rWGS section (III)

FIG. 4a illustrates a schematic layout of another embodiment of a plant,in which the syngas stage comprises an rWGS section (III) plus an ATRsection (I). In this layout, rWGS section (III) and ATR section (I) areparallel to each other. Reference numbers are as for the previousfigures, plus:

-   50 syngas stream from ATR section (I)

FIG. 4b illustrates a schematic layout of another embodiment of a plant,as per FIG. 4a . In the layout of FIG. 4b , the syngas stream 50 fromthe ATR section (I) is arranged to heat the rWGS section (III). Effluentfrom ATR section (I) gets cooled to become syngas stream 60 byexchanging heat with rWGS section and then is combined with the syngasstream 40 from the rWGS section (III).

-   60 cooled syngas stream from ATR section (I) after cooling in rWGS    section (III)

FIGS. 4c corresponds to FIG. 4a , in which a methanation stage (II) ispresent instead of the rWGS section (III).

FIG. 5 illustrates a schematic layout of another embodiment of a plant,in which a component recovery stage (C)—i.e. recycle of either hydrogenor more CO₂—is present between the syngas stage (A) and the synthesisstage (B). Reference numbers are as for the previous figures, plus:

-   C component recovery stage-   150 recycle gas from component recovery stage-   200 syngas from component recovery stage

EXAMPLES

Various syngas stages are compared based on their effectiveness ofutilizing carbon feedstock and energy. In recent years, CO₂ emissionsfrom such syngas stages have also been compared to minimize theenvironmental impact.

Conventionally, hydrocarbon-based feed is primarily used in syngas stage(A). Typical values of abovementioned distinguishing factors from suchsyngas stages, consisting of autothermal reformer (ATR) section (I), areshown in table 1.

In C1, values from a conventionally designed hydrocarbon-based syngasstage (A) without CO₂ feed are shown. In C2, some H₂ and CO₂ feed areused along with hydrocarbon feed. Hydrocarbon feed is still higher thanCO₂ feed. In C3, more CO₂ and H₂ feed are used such that CO₂ feedconsumption becomes higher than hydrocarbon feed consumption.

TABLE 1 Parameters Unit C1 C2 C3 H₂ content in first feed (1) mol % N/A99.0 99.0 CO₂ content in second feed (2) mol % N/A 99.9 99.9 First feed(1)/second feed (2) — N/A 2.97 2.97 External third feed (3a)/ — N/A 1.340.39 second feed (2) Fourth feed (4)/first feed (1) — N/A 0.38 0.22Fifth feed (5)/first feed (1) — N/A 0.31 0.12 H₂/CO in syngas product(100) — 1.91 2.08 1.97 CO in syngas product (100)/ % 77.11 74.46 71.80total C in feeds (both external and internal streams) Relative CO₂emission % 100.00 61.42 28.31 in syngas stage (A)/1000 Nm³ (H₂ + CO)product

As it can be seen, CO₂ emission improve with higher CO₂ feedconsumption. However, conversion is reduced to some extent.

This challenge can be solved by including methanation section (II) inaddition to the ATR section (I) in the syngas stage (A). In table 2, thekey parameters for the syngas stage (A) are provided, wherein the syngasstage consists of a methanation section (II) followed by an ATR section(I). Syngas produced in the syngas stage (A) is fed to synthesis stage(B), comprising a Fischer-Tropsch synthesis section and product work-upsection. Some of the recycle streams from synthesis stage (B) are usedinternally in the syngas stage (A).

TABLE 2 Parameters Unit C4 C5 C6 H₂ content in first feed (1) mol % 99.099.0 99.0 CO₂ content in second feed (2) mol % 99.9 99.9 99.9 First feed(l)/second feed (2) — 4.95 4.51 4.01 External third feed (3a)/ — 0.280.14 0.06 second feed (2) Fourth feed (4)/first feed (1) — 0.17 0.160.16 Fifth feed (5)/first feed (1) — 0.03 0.03 0.04 H₂/CO in syngasproduct (100) — 2.41 2.18 1.95 CO in syngas product (100)/ % 80.80 80.6079.68 total C in feeds (both external and internal streams) Relative CO₂emission % 0.00 0.00 0.00 in syngas stage (A)/1000 Nm³ (H₂ + CO) product

In this concept no hydrocarbon combustion takes place and this there areno CO₂ emissions.

Specific net energy consumption in the syngas stage is estimated basedon 1 Nm³ of (H₂+CO) in the product stream. In table 1 and 2, relativeCO₂ emission is estimated with respect to CO₂ emission in C1 as basis.

The following numbered aspects are provided:

Aspect 1. A plant, said plant comprising:

-   -   a. a syngas stage, said syngas stage comprising an autothermal        reforming (ATR) section, and;    -   b. a synthesis stage;        said plant comprising:    -   a first feed comprising hydrogen to the syngas stage;    -   a second feed comprising carbon dioxide to the syngas stage;    -   a third feed comprising hydrocarbons to the syngas stage,        upstream of said ATR section; and    -   a fourth feed comprising oxygen to the ATR section;        wherein said syngas stage is arranged to provide a syngas stream        and feed said syngas stream to the synthesis stage.

Aspect 2. The plant according to aspect 1, wherein said third feedcomprising hydrocarbons is fed to the syngas stage, directly upstream ofsaid ATR section.

Aspect 3. The plant according to any one of the preceding aspects,wherein the syngas stream is fed directly from the syngas stage to thesynthesis stage.

Aspect 4. The plant according to any one of aspects 1-2, wherein theplant comprises a post-conversion section, located between said syngasstage and said synthesis stage, and a CO₂ feed to said post-conversionsection, arranged to be mixed with the syngas stream between the syngasstage and the post-conversion section.

Aspect 5. The plant according to any one of the preceding aspects,further comprising a fifth steam feed to the syngas stage.

Aspect 6. The plant according to any one of the preceding aspects,wherein said syngas stage consists of said autothermal reforming (ATR)section, and wherein first, second, third and fourth feeds are fed tosaid ATR section.

Aspect 7. The plant according to any one of aspects 1-5, wherein thesyngas stage additionally comprises a methanation section arrangedupstream the ATR section; wherein a part or all of the first feed is fedto the methanation section; a part or all of the second feed is fed tothe methanation section; and wherein a part or all of the third feed isfed to the syngas stage; upstream said methanation section and/orbetween said methanation section and said ATR section.

Aspect 8. The plant according to aspect 7, wherein the methanationsection comprises two or more methanation units, such as three or moremethanation units.

Aspect 9. The plant according to aspect 8, wherein parts of the firstfeed comprising hydrogen are fed separately to different methanationunits in the methanation section; or the entire first feed comprisinghydrogen is fed together to the methanation unit located furthestupstream in the methanation section.

Aspect 10. The plant according to any one of aspects 8-9, wherein partsof the second feed comprising carbon dioxide are fed separately todifferent methanation units in the methanation section; or the entiresecond feed comprising carbon dioxide is fed together to the methanationunit located furthest upstream in the methanation section.

Aspect 11. The plant according to any one of aspects 8-10, wherein partsof the third feed comprising hydrocarbons are fed separately todifferent methanation units in the methanation section; or the entirethird feed comprising hydrocarbons is fed together to one methanationunit in the methanation section.

Aspect 12. The plant according to any one of aspects 8-11, wherein apart of the effluent from one methanation unit is cooled and recycled tothe inlet of said methanation unit and/or to the inlet of any additionalmethanation units located upstream said one methanation unit.

Aspect 13. The plant according to any one of aspects 1-5 and 7-12,wherein the syngas stage additionally comprises a reverse water gasshift (rWGS) section upstream the ATR section wherein a part or all ofthe first feed is fed to the rWGS section; a part or all of the secondfeed is fed to the rWGS section; and wherein a part or all of the thirdfeed is fed to the syngas stage between said rWGS section (III) and saidATR section.

Aspect 14. The plant according to aspect 13, wherein the rWGS sectioncomprises two or more rWGS units, such as three or more rWGS units.

Aspect 15. The plant according to aspect 14, wherein parts of the firstfeed comprising hydrogen are fed separately to different rWGS units inthe rWGS section; or the entire first feed comprising hydrogen is fedtogether to the reverse WGS unit located furthest upstream in the rWGSsection.

Aspect 16. The plant according to any one of aspects 14-15, whereinparts of the second feed comprising carbon dioxide are fed separately todifferent rWGS units in the rWGS section; or the entire second feedcomprising carbon dioxide is fed all together to the rWGS unit locatedfurthest upstream in the rWGS section.

Aspect 17. The plant according to any one of the preceding aspects,wherein the syngas stream at the inlet of said synthesis stage has ahydrogen/carbon monoxide ratio in the range 1.00-4.00; preferably1.50-3.00, more preferably 1.50-2.10.

Aspect 18. The plant according to any one of the preceding aspects,wherein the syngas stream at the outlet of said syngas stage has amodule, as defined above, in the range 1.50-2.50; preferably 1.80-2.30,more preferably 1.90-2.20.

Aspect 19. The plant according to any one of the preceding aspects,wherein the ratio of H₂:CO₂ provided at the plant inlet is between1.0-9.0, preferably 2.5-8.0, more preferably 3.0-7.0.

Aspect 20. The plant according to any one of the preceding aspects,wherein the synthesis stage is a Fischer-Tropsch (F-T) stage, andwherein the ratio of H₂:CO₂ provided at the plant inlet is in the rangeof 3.0-7.0 or more preferably from 3.0-6.0 and most preferably 3.0-5.0.

Aspect 21. The plant according to any one of the preceding aspects,wherein the first feed consists essentially of hydrogen, i.e. over 75%,such as over 85%, preferably over 90%, more preferably over 95%, evenmore preferably over 99% of the first feed is hydrogen.

Aspect 22. The plant according to any one of the preceding aspects,wherein the second feed consists essentially of carbon dioxide, i.e.over 75%, such as over 85%, preferably over 90%, more preferably over95%, even more preferably over 99% of the second feed is carbon dioxide.

Aspect 23. The plant according to any one of the preceding aspects,wherein said third feed comprises one or more hydrocarbons selected frommethane, ethane, propane or butane.

Aspect 24. The plant according to any one of the preceding aspects,wherein said third feed comprising hydrocarbons is a natural gas feed.

Aspect 25. The plant according to any one of the preceding aspects,wherein said third feed additionally comprises CO₂ and/or CO and/or H₂.

Aspect 26. The plant according to any one of the preceding aspects,wherein the fourth feed consists essentially of oxygen, i.e. over 75%such as over 90% or over 95%, such as over 99% of the fourth feed isoxygen.

Aspect 27. The plant according to any one of the preceding aspects,wherein the fourth feed additionally comprises steam.

Aspect 28. The plant according to any one of the preceding aspects,wherein the synthesis stage is arranged to convert said syngas streaminto at least a product stream and, optionally, a hydrocarbon-containingoff-gas stream.

Aspect 29. The plant according to aspect 28, wherein at least a portionof said hydrocarbon-containing off-gas stream is fed to the syngas stagein addition to said third feed comprising hydrocarbons.

Aspect 30. The plant according to any one of the preceding aspects,wherein the synthesis stage is a Fischer-Tropsch (F-T) stage arranged toconvert said syngas stream into at least a hydrocarbon product streamand a hydrocarbon-containing off-gas stream in the form of an F-T tailgas stream.

Aspect 31. The plant according to any one of the preceding aspects,wherein the synthesis stage is a Fischer-Tropsch (F-T) stage arranged toconvert said syngas stream into at least a hydrocarbon product stream,being a diesel stream; and an LPG and/or a naphtha product stream, andwherein at least a portion of said LPG and/or a naphtha product streamis fed to the syngas stage in addition to said third feed comprisinghydrocarbons.

Aspect 32. The plant according to any one of aspects 1-31, in which thesynthesis stage comprises at least one methanol synthesis stage arrangedto provide at least a methanol product stream.

Aspect 33. The plant according to aspect 32, in which the synthesisstage further comprises a methanol-to-gasoline (MTG) synthesis stagearranged to receive the methanol product stream from the methanolsynthesis stage and convert it to at least a gasoline stream and an LPGproduct stream, and wherein, optionally, a portion of said LPG productstream is fed to the syngas stage in addition to said third feedcomprising hydrocarbons.

Aspect 34. The plant according to any one of the preceding aspects,wherein when the third feed is a LPG and/or a naphtha product stream ora natural gas feed said plant further comprises a pre-reforming section,arranged in the third feed, upstream the syngas stage.

Aspect 35. The plant according to aspect 34, wherein the hydrocarbonproduct stream is an LPG and/or a naphtha product stream from an F-Tstage, and wherein said LPG and/or naphtha product stream is passedthrough said pre-reforming section prior to being fed to the syngasstage.

Aspect 36. The plant according to any one of aspects 34-35, whereineffluent gas from the ATR section is arranged to heat the pre-reformingsection.

Aspect 37. The plant according to any one of the preceding aspects,further comprising an electrolyser arranged to convert water or steaminto at least a hydrogen-containing stream and an oxygen-containingstream, and wherein at least a part of said hydrogen-containing streamfrom the electrolyser is fed to the syngas stage as said first feedand/or wherein at least a part of said oxygen-containing stream from theelectrolyser is fed to the syngas stage as said fourth feed.

Aspect 38. The plant according to aspect 37, wherein the water or steamfed to the electrolyser is obtained from one or more units or stages insaid plant.

Aspect 39. The plant according to any one of the preceding aspects,comprising a sixth feed of hydrogen to the syngas stream, upstream thesynthesis stage.

Aspect 40. The plant according to aspect 39, wherein at least a part ofsaid hydrogen-containing stream from the electrolyser is fed to thesyngas stream, upstream the synthesis stage as said sixth feed ofhydrogen.

Aspect 41. The plant according to any one of aspects 31-40, wherein whenthe third feed is an off-gas stream said plant further comprises ahydrogenator arranged to hydrogenate the third feed, before said thirdfeed enters the syngas stage.

Aspect 42. The plant according to any one of the preceding aspects,further comprising a hydrogen removal section, located between saidsyngas stage and said synthesis stage, and arranged to remove at least apart of the hydrogen from the syngas stream.

Aspect 43. The plant according to aspect 42, wherein at least a portionof the hydrogen removed from the syngas stream in said hydrogen removalsection is compressed and fed as said first feed to the syngas stage.

Aspect 44. The plant according to any one of the preceding aspects,further comprising a carbon dioxide removal section, located betweensaid syngas stage and said synthesis stage, and arranged to remove atleast a part of the carbon dioxide from the syngas stream.

Aspect 45. The plant according to aspect 44, wherein at least a portionof the carbon dioxide removed from the syngas stream in said carbondioxide removal section is compressed and fed as said second feed to thesyngas stage.

Aspect 46. The plant according to any one of the preceding aspectswherein the ratio of moles of carbon in the third feed comprisinghydrocarbons, when external to the plant, to the moles of carbon in CO₂in the second feed is less than 0.3, preferably less than 0.25 and morepreferably less than 0.2 or even lower than 0.1.

Aspect 47. The plant according to any one of the preceding aspects,wherein the syngas stage additionally comprises a reverse water gasshift (rWGS) section and a methanation section; and wherein the reversewater gas shift (rWGS) section is arranged upstream the methanationsection and the methanation section is arranged upstream the ATRsection.

Aspect 48. The plant according to any one of the preceding aspects,wherein

-   -   the syngas stage (A) comprises a methanation section (II)        arranged in parallel to said ATR section (I);    -   wherein at least a portion of the first feed (1) and at least a        portion of the second feed (2) are arranged to be fed to the        methanation section (II) and said methanation section (II) is        arranged to convert said at least a portion of the first feed        (1) and at least a portion of the second feed (2) to a first        syngas stream (40);    -   wherein a third feed (3) comprising hydrocarbons and a fourth        feed (4) comprising oxygen are arranged to be fed to the ATR        section (I); and wherein said ATR section (I) is arranged to        convert said third feed (3) comprising hydrocarbons and said        fourth feed (4) comprising oxygen to a second syngas stream (50)    -   wherein the first syngas stream (40) from the methanation        section (II) is arranged to be combined with the second syngas        stream (50) from the ATR section (I); and the combined syngas        stream (100) is arranged to be fed to the synthesis stage (B).

Aspect 49. The plant according to any one of the preceding aspects,wherein

-   -   the syngas stage (A) comprises a reverse water gas shift (rWGS)        section (III) arranged in parallel to said ATR section (I);    -   wherein at least a portion of the first feed (1) and at least a        portion of the second feed (2) are arranged to be fed to the        rWGS section (III) and said rWGS section (III) is arranged to        convert said at least a portion of the first feed (1) and at        least a portion of the second feed (2) to a first syngas stream        (40);    -   wherein a third feed (3) comprising hydrocarbons and a fourth        feed (4) comprising oxygen are arranged to be fed to the ATR        section (I); and wherein said ATR section (I) is arranged to        convert said third feed (3) comprising hydrocarbons and said        fourth feed (4) comprising oxygen to a second syngas stream (50)    -   wherein the first syngas stream (40) from the rWGS section (III)        is arranged to be combined with the second syngas stream (50)        from the ATR section (I); and the combined syngas stream (100)        is arranged to be fed to the synthesis stage (B).

Aspect 50. The plant according to aspect 48 or 49, wherein beforecombining first and second syngas streams, the second syngas stream (50)from the ATR section (I) is arranged to provide at least a part of theenergy required for the endothermic reaction in the rWGS section (III).

Aspect 51. A method for producing a product stream, said methodcomprising the steps of:

-   -   providing a plant as defined in any one of the preceding        aspects;    -   supplying a first feed comprising hydrogen to the syngas stage;    -   supplying a second feed comprising carbon dioxide to the syngas        stage;    -   supplying a third feed comprising hydrocarbons to the syngas        stage, upstream of said ATR section;    -   supplying a fourth feed comprising oxygen to the ATR section;    -   providing a syngas stream (100) in said syngas stage (A) from at        least said first, second, third and fourth feeds, and feeding        said syngas stream (100) to the synthesis stage (B);    -   converting said syngas stream (100) into at least a product        stream (500) and a hydrocarbon-containing off-gas stream (3 b)        in said synthesis stage (B); and    -   optionally, feeding at least a portion of said        hydrocarbon-containing off-gas stream (3 b) to the syngas        stage (I) in addition to said third feed (3) comprising        hydrocarbons; upstream of said ATR section (I).

Aspect 52. The method according to aspect 51, in which the synthesisstage is a Fischer-Tropsch (F-T) stage arranged to convert said syngasstream into at least a hydrocarbon product stream and ahydrocarbon-containing off-gas stream in the form of an F-T tail gasstream.

Aspect 53. The method according to any one of aspects 51-52, wherein thecontent of methane in the synthesis gas sent to the synthesis stage isless than 5%, such as less than 3% or even less than 2%.

The present invention has been described with reference to a number offeatures, aspects and embodiments. These can be combined by the skilledperson at will, within the scope of the present invention withoutdeparting from the scope of the invention as defined in the claims.

1. A method for producing a product stream, said method comprising thesteps of: providing a plant, said plant comprising: a. a syngas stage,said syngas stage comprising an autothermal reforming (ATR) section,and; b. a synthesis stage; said plant comprising: a first feedcomprising hydrogen to the syngas stage; a second feed comprising carbondioxide to the syngas stage; a third feed comprising hydrocarbons to thesyngas stage, upstream of said ATR section; and a fourth feed comprisingoxygen to the ATR section; wherein said syngas stage is arranged toprovide a syngas stream and feed said syngas stream to the synthesisstage; supplying a first feed comprising hydrogen to the syngas stage;supplying a second feed comprising carbon dioxide to the syngas stage;supplying a third feed comprising hydrocarbons to the syngas stage,upstream of said ATR section; supplying a fourth feed comprising oxygento the ATR section; providing a syngas stream in said syngas stage fromat least said first, second, third and fourth feeds, and feeding saidsyngas stream to the synthesis stage; converting said syngas stream intoat least a product stream and a hydrocarbon-containing off-gas stream insaid synthesis stage; wherein the ratio of moles of carbon in the thirdfeed comprising hydrocarbons, when external to the plant, to the molesof carbon in CO2 in the second feed is less than 0.5.
 2. The methodaccording to claim 1, wherein the ratio of moles of carbon in the thirdfeed comprising hydrocarbons, when external to the plant, to the molesof carbon in CO₂ in the second feed is less than 0.3.
 3. The methodaccording to claim 1, further comprising the step of feeding at least aportion of said hydrocarbon-containing off-gas stream to the syngasstage in addition to said third feed comprising hydrocarbons; upstreamof said ATR section.
 4. The method according to claim 1, wherein thesyngas stream at the inlet of said synthesis stage has a hydrogen/carbonmonoxide ratio in the range 1.00-4.00.
 5. The method according towherein the ratio of H2:CO2 provided at the plant inlet is between1.0-9.0.
 6. The method according to claim 5, wherein the synthesis stageis an FT synthesis stage and the H2:CO2-ratio at the plant inlet is inthe range of 3.0-7.0.
 7. The method according to claim 1, wherein saidsyngas stage consists of said autothermal reforming (ATR) section, andwherein first, second, third and fourth feeds are fed directly to saidATR section.
 8. The method according to claim 1, wherein the syngasstage additionally comprises a methanation section arranged upstream theATR section; wherein a part or all of the first feed is fed to themethanation section; a part or all of the second feed is fed to themethanation section; and wherein a part or all of the third feed is fedto the syngas stage; upstream said methanation section or between saidmethanation section and said ATR section.
 9. The method according toclaim 1, wherein the syngas stage additionally comprises a reverse watergas shift (rWGS) section upstream the ATR section wherein a part or allof the first feed is fed to the rWGS section; a part or all of thesecond feed is fed to the rWGS section; and wherein a part or all of thethird feed is fed to the syngas stage between said rWGS section and saidATR section.
 10. The method according to claim 1, wherein; the syngasstage comprises a reverse water gas shift (rWGS) section arranged inparallel to said ATR section; wherein at least a portion of the firstfeed and at least a portion of the second feed are arranged to be fed tothe rWGS section and said rWGS section is arranged to convert said atleast a portion of the first feed and at least a portion of the secondfeed to a first syngas stream; wherein a third feed comprisinghydrocarbons and a fourth feed comprising oxygen are arranged to be fedto the ATR section; and wherein said ATR section is arranged to convertsaid third feed comprising hydrocarbons and said fourth feed comprisingoxygen to a second syngas stream wherein the first syngas stream fromthe rWGS section is arranged to be combined with the second syngasstream from the ATR section; and the combined syngas stream is arrangedto be fed to the synthesis stage.
 11. A plant, said plant comprising: a.a syngas stage, said syngas stage comprising an autothermal reforming(ATR) section, and; b. a synthesis stage; said plant comprising: a firstfeed comprising hydrogen to the syngas stage; a second feed comprisingcarbon dioxide to the syngas stage; a third feed comprising hydrocarbonsto the syngas stage, upstream of said ATR section; and a fourth feedcomprising oxygen to the ATR section; wherein said syngas stage isarranged to provide a syngas stream and feed said syngas stream to thesynthesis stage; and wherein; the syngas stage additionally comprises amethanation section arranged upstream the ATR section; wherein a part orall of the first feed is fed to the methanation section; a part or allof the second feed is fed to the methanation section; and wherein a partor all of the third feed is fed to the syngas stage; upstream saidmethanation section or between said methanation section and said ATRsection.
 12. A plant, said plant comprising: a. a syngas stage, saidsyngas stage comprising an autothermal reforming (ATR) section, and; b.a synthesis stage; said plant comprising: a first feed comprisinghydrogen to the syngas stage; a second feed comprising carbon dioxide tothe syngas stage; a third feed comprising hydrocarbons to the syngasstage, upstream of said ATR section; and a fourth feed comprising oxygento the ATR section; wherein said syngas stage is arranged to provide asyngas stream and feed said syngas stream to the synthesis stage; andwherein; the syngas stage additionally comprises a reverse water gasshift (rWGS) section upstream the ATR section wherein a part or all ofthe first feed is fed to the rWGS section; a part or all of the secondfeed is fed to the rWGS section; and wherein a part or all of the thirdfeed is fed to the syngas stage between said rWGS section and said ATRsection.
 13. A plant, said plant comprising: a. a syngas stage, saidsyngas stage comprising an autothermal reforming section, and; b. asynthesis stage; said plant comprising: a first feed comprising hydrogento the syngas stage; a second feed comprising carbon dioxide to thesyngas stage; a third feed comprising hydrocarbons to the syngas stage,upstream of said ATR section; and a fourth feed comprising oxygen to theATR section; wherein said syngas stage is arranged to provide a syngasstream and feed said syngas stream to the synthesis stage; and wherein;the syngas stage comprises a methanation section arranged in parallel tosaid ATR section; wherein at least a portion of the first feed and atleast a portion of the second feed are arranged to be fed to themethanation section and said methanation section is arranged to convertsaid at least a portion of the first feed and at least a portion of thesecond feed to a first syngas stream; wherein a third feed comprisinghydrocarbons and a fourth feed comprising oxygen are arranged to be fedto the ATR section; and wherein said ATR section is arranged to convertsaid third feed comprising hydrocarbons and said fourth feed comprisingoxygen to a second syngas stream, wherein the first syngas stream fromthe methanation section is arranged to be combined with the secondsyngas stream from the ATR section; and the combined syngas stream isarranged to be fed to the synthesis stage.
 14. A plant, said plantcomprising: a. a syngas stage, said syngas stage comprising anautothermal reforming (ATR) section, and; b. a synthesis stage; saidplant comprising: a first feed comprising hydrogen to the syngas stage;a second feed comprising carbon dioxide to the syngas stage; a thirdfeed comprising hydrocarbons to the syngas stage, upstream of said ATRsection; and a fourth feed comprising oxygen to the ATR section; whereinsaid syngas stage is arranged to provide a syngas stream and feed saidsyngas stream to the synthesis stage; and wherein; the syngas stagecomprises an rWGS section arranged in parallel to said ATR section;wherein at least a portion of the first feed and at least a portion ofthe second feed are arranged to be fed to the rWGS section and said rWGSsection is arranged to convert said at least a portion of the first feedand at least a portion of the second feed to a first syngas stream;wherein a third feed comprising hydrocarbons and a fourth feedcomprising oxygen are arranged to be fed to the ATR section; and whereinsaid ATR section is arranged to convert said third feed comprisinghydrocarbons and said fourth feed-comprising oxygen to a second syngasstream wherein the first syngas stream from the rWGS section is arrangedto be combined with the second syngas stream from the ATR section; andthe combined syngas stream is arranged to be fed to the synthesis stage.15. The method according to claim 1, wherein said third feed comprisinghydrocarbons is fed to the syngas stage, directly upstream of said ATRsection.
 16. The method according to claim 1, further comprising a fifthsteam feed to the syngas stage.
 17. The method according to claim 1,wherein said third feed comprising hydrocarbons is a natural gas feed.18. The method according to claim 1, wherein the synthesis staged isarranged to convert said syngas stream into at least a product streamand, optionally, a hydrocarbon-containing off-gas stream.
 19. The methodaccording to claim 1, wherein at least a portion of saidhydrocarbon-containing off-gas stream is fed to the syngas stage inaddition to said third feed comprising hydrocarbons.
 20. The methodaccording to claim 1, wherein the synthesis stage is a Fischer-Tropsch(F-T) stage arranged to convert said syngas stream into at least ahydrocarbon product stream and a hydrocarbon-containing off-gas streamin the form of an F-T tail gas stream.
 21. The method according to claim1, wherein the synthesis stage, comprises a methanol synthesis stagearranged to provide at least a methanol product stream.
 22. The methodaccording to claim 1, further comprising an electrolyser arranged toconvert water or steam into at least a hydrogen-containing stream and anoxygen-containing stream, and wherein at least a part of saidhydrogen-containing stream from the electrolyser is fed to the syngasstage as said first feed and/or wherein at least a part of saidoxygen-containing stream from the electrolyser is fed to the syngasstage as said fourth feed.
 23. The method according to claim 1, furthercomprising a sixth feed comprising hydrogen to the syngas stream,upstream the synthesis stage.
 24. The method according to claim 1,wherein before being combined with first and second syngas streams thesyngas stream from the ATR section is arranged to provide at least apart of the energy required for the endothermic reaction in the rWGSsection.
 25. The method according to claim 1, wherein the synthesisstage is a Fischer-Tropsch (F-T) stage arranged to convert said syngasstream into at least a hydrocarbon product stream and ahydrocarbon-containing off-gas stream in the form of an F-T tail gasstream.